Refractory ramming mix compositions containing a relatively high percentage of alumina chemically bound by phosphoric acid or an aluminum phosphate are well known in the art, particularly as described in the following patents: Salizar U.S. Pat. No. 3,547,664; Noda, et al. U.S. Pat. Nos. 3,958,582 and 3,891,009; Beeler U.S. Pat. No. 4,177,308; and Erskine U.S. Pat. No. 4,248,810. In some of these patents, an insulating material, such as perlite, is included to provide a light, temperature resistant refractory heat-insulating composition. The compositions generally are mixed to the consistency of a paste or mortar consistency so that the composition can be mixed, spread into a desired shape and sliced to form a slab of predetermined dimensions before the slices or slabs are rammed or pounded into place in a moist condition to physically and chemically form a monolithic refractory lining. The lining is then heated to drive off the moisture and heated at high temperature to form the final set or ceramic bond necessary in a refractory lining.
As set forth in my prior U.S. Pat. No. 3,547,664, two of the biggest problems in prior art high alumina ramming mixes are cracking upon drying and a need for higher strength at temperatures in which a mix must relay upon a chemical bond before the ceramic bond is formed. In accordance with my prior patent, I found that including ceramic fibers in an amount of about 2-6% by weight of clay in the mix provides a stronger ramming mix which does not crack upon drying.
Another problem with a prior art high alumina ramming mixes, particularly prevalent in chemically bound ramming mixes, is the inability to provide a ramming mix which has a shelf life of more than about three weeks. After a chemically bound ramming mix is sliced to form a slab of predetermined dimensions, the ramming mix begins to dry as a result of ambient conditions and, particularly, where a chemical binder such as aluminum phosphate is being formed in situ such as described in my prior U.S. Pat. No. 3,547,664, where phosphoric acid reacts with alumina to form the aluminum phosphate binder. This in situ reaction between phosphoric acid and alumina is exothermic resulting in moisture being driven away from the ramming mix. The ramming mix must be moist when rammed or pounded into position as a lining and, therefore, ramming mixes of the prior art generally have had a shelf life of about three weeks or less. Liquid aluminum phosphate has been added as the chemical binder in some prior art refractory ramming mixes and, generally, since these refractory ramming mixes do not depend upon an in situ reaction for the formation of the aluminum phosphate binder, it has been found that the shelf life problem is not as severe. However, no prior art refractory ramming mixes using a chemical binder will remain sufficiently wet for ramming or pounding into place significantly more than about three weeks.